they got it from hadith , all fiqahs base their prayer methods on hadith and there is a huge overlap even between sunni fiqahs and jafari fiqah they have their sources good or bad authentic or not that is another debate
where can we find your way of praying thats the question ?
thats their problem they didnt preserve the seerah of their Prophets and corrupted the texts thats why Quran was sent down with Muhammad to remove the inovations and straighten the deen again
3.113-115. Not all of them are alike: Of the People of the Book are a portion that stand (For the right): They rehearse the Signs of Allah all night long, and they prostrate themselves in adoration. They believe in Allah and the Last Day; they enjoin what is right, and forbid what is wrong; and they hasten (in emulation) in (all) good works: They are in the ranks of the righteous. Of the good that they do, nothing will be rejected of them; for Allah knoweth well those that do right
How do these people prostrate? Do they do it like the Muslim sects do?
22.34 To every people did We appoint rites (of sacrifice), that they might celebrate the name of Allah over the sustenance He gave them from animals (fit for food). But your Allah is One Allah. submit then your wills to Him (in Islam): and give thou the good news to those who humble themselves,-
22.18 Seest thou not that to Allah bow down in worship all things that are in the heavens and on earth,- the sun, the moon, the stars; the hills, the trees, the animals; and a great number among mankind? But a great number are (also) such as are fit for Punishment: and such as Allah shall disgrace,- None can raise to honour: for Allah carries out all that He wills.
22.26 Behold! We gave the site, to Abraham, of the (Sacred) House, (saying): "Associate not anything (in worship) with Me; and sanctify My House for those who compass it round, or stand up, or bow, or prostrate themselves (therein in prayer).
22.37 It is not their meat nor their blood, that reaches Allah. it is your piety that reaches Him: He has thus made them subject to you, that ye may glorify Allah for His Guidance to you and proclaim the good news to all who do right.
22.40 (They are) those who have been expelled from their homes in defiance of right,- (for no cause) except that they say, "our Lord is Allah.. Did not Allah check one set of people by means of another, there would surely have been pulled down monasteries, churches, synagogues, and mosques, in which the name of Allah is commemorated in abundant measure. Allah will certainly aid those who aid his (cause);- for verily Allah is full of Strength, Exalted in Might, (able to enforce His Will).
So whats this? Who is this talking about then?
5.46. And in their footsteps We sent Jesus the son of Mary, confirming the Law that had come before him: We sent him the Gospel: therein was guidance and light, and confirmation of the Law that had come before him: a guidance and an admonition to those who fear Allah.
****5.48 Let the people of the Gospel judge by what Allah hath revealed therein. If any do fail to judge by (the light of) what Allah hath revealed, they are (no better than) those who rebel
Which scriptures is this talking about then?